Electric switching



Nov. 29, 1938. -J. BIERMANNS ELECTRIC SWITCHING Original Filed June 22, 1936 Inventor: Josef BieP-manns,

His Attorney.

Patented Nov. 29, 1938 UNITED STATES 2.138.652 Emo'mic swrronmo Josef Blermanns, Berlin-Johannisthal, Germany, assignor to General Electric Company, a corporation of New York Application June22, 1936, Serial No. 86,680. Re-

newed March 17, 1938. In Germany July 10,

My invention relates to electric switching and more particularly to means for changing transformer taps under load.

It is often desirable to change transformer taps under load for this provides a convenient way of varying the transformer ratio for regulating purposes. Various ways of doing this are old and well known in the art.

The principal problem in changing transformer taps under load is the electric switching problem of transferring the current in an electric circuit from one point thereon to another. For best operation this current transfer should of course be made without interruption of the current and preferably with the productionof the lowest possible voltage drop so as to minimize electrical disturbancesin the circuit during switching.

In accordance with my invention I provide an electric switching arrangement of this character which is well adapted for transformer tap changing under load but which of course is not limited to such application. It may be described as the equivalent of a multi-throw switch having separate negative impedance-current characteristic impedances (devices whose impedance decreases as the current through them, or the voltage across them, or both, increases) connected across the throws thereof. With such an arrangement, when the switch is in-one contact making position one of the negative impedance-current characteristic impedances is short circuited and practically all of the circuit current flows through the switch. If there is a potential between the points between which the current is to be switched this current will be impressed upon the non-short circuited negative impedance or impedances, depending upon the number of throws the switch has, and this impedance is so constructed that it permits the flow of but a negligible current with the application of such a potential. During a switch positional change, however, an arc is first drawn when the contacts of the switch separate. As this arc is drawn out the voltage across it increases thereby increasing the voltage across the negative impedances, which consequently have an increased current flow through them thereby reducing their impedance until the point is reached at which the arc is extinguished and the circuit current is divided between the impedances. These impedances are so designed that they can divide the full load current of the circult with the production of but a relatively small voltage drop. When a switch positional change has been completed the switch will short circuit 6 Claims. (01. 171-119 the other impedance and the current will be transferred to another point on the circuit.

An object of my invention is to provide a new and improved electric switching arrangement.

Another object of my invention is to provide a new and improved arrangement for transformer tap changing under load.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the .drawing Fig. 1 is a simplified diagrammatic showing of one embodiment of my invention, Fig. 2 shows a modification thereof and Fig. 3 shows diagrammatically a regulating system embodying another form of my invention.

Referring now to the drawing and more particularly to Fig. 1, there is shown therein a transformer winding I provided with taps 2. The winding .l is connected in a circuit 3 and interposed between the winding 1 and the circuit 3 is a tap changing switch 4 having fixed contacts 5 and 6 connected respectively to two of the taps on the winding I and having a movable contact carrying member i which is pivotally mounted about a point 8 so that it can make selective contact making engagement with the fixed contacts 5 and 6. It will be seen that the switch 4 is the equivalent of a single pole double throw. switch, the only diflference being that the movable memher i is a V-shaped member carrying two contacts instead of being a simple straight member having one contact. One throw of the switch is between fixed contact 5 and the common point 8 while the other throw is between the other fixed contact 6 and the common point 8.

Connected respectively across the throws of the switch 4 are a pair of negative impedance current characteristic impedances 9 and It. These 1m pedances may be of any suitable type, one form of which is the ceramic resistance material disponential manner with increases in current therethrough or voltage thereacross.

In the operation of Fig. 1, when the movable contact member 1 is engaging fixed contact 5 substantially all of the circuit current flows through these contacts and the resistance 9 is short circuited. Resistance I0 is so constructed and proportioned that at the voltage between the taps to which the contacts 5 and 6 are connected,

and which voltage will consequently be applied across the resistance In, the current through this resistance will be very low and substantially negligible. If now the movable contact is rotated about the pivot point 8 in a clockwise direction an arc will first be drawn from the movable contact I to the fixed contact 5 and this are will carry substantially all of the circuit current. However, as the arc is drawn out the voltage across both the resistances 9 and ID will increase until when the arc goes out all of the circuit current will be divided between the resistances 9 and Ill. These resistances are so constructed that they are capable of dividing the full circuit current at a relatively low over-all voltage drop. This is because as the current through these resistances increases their resistance decreases very rapidly so that the voltage drop, which is proportional to the product of the resistance and the current will be low. As soon as the movable contact I engages the fixed contact 6 substantially all of the circuit current will be transferred to the fixed contact 6, and consequently to the transformer tap to which this contact is connected. The resistance [0 will now be short circuited and the tap voltage will be applied across resistance 9 which, being similar to resistance ID, will prevent the flow of all but a negligible amount of current therethrough.

In the modification shown in Fig. 2 the tap changing switch is of the electromagnetically operated contactor type. The parts of the switch corresponding to the parts of Fig. 1 are marked by corresponding but primed reference characters. The movable contact member I bridges two sets of fixed contacts 5' and 6, one of each set corresponding to the contacts 5 and 6 of the switch of Fig. 1 and being connected to two of the taps on the winding l. The point 8' in Fig. 2 corresponds to the common electrical point 8 in Fig. l.

It is not essential that the switch employed in my invention be a single pole switch and as shown in Fig. 2, another pole II has been added in the other conductor of the circuit 3. However. it will of course be understood that any multipole switch necessarily includes in it a single pole switch.

shunting, or connected in parallel with, the various throws of the switch in Fig. 2 are negative impedance-current characteristic devices [2, l3 and I4 in the form of self-saturating iron core reactors.

In the operation of Fig. 2 with-the parts in the position shown in the drawing, thecircuit current is practically all flowing through switch contacts 6' and the only current flowing through the reactors is the current flowing through reactor l2 which is produced by the voltage between the taps to which the fixed contacts 5' and 6' are connected. The reactor, however, may be designed so as to have a very high reactance for the small current produced by this relatively low voltage. However, when the contactor is energized by any suitable means (not shown) and moved upwardly the current flowing through the bridging contact cooperating with the fixed contact 6' will be interrupted as will also the current flowing through the bridging contact of the throw H of the switch. Consequently, all of the circuit current will divide through the reactors l2 and II with respect to one throw of the switch and all of the return current will flow through the reactor l4. This relatively high circuit current will cause saturation in the reactors thereby reducing their reactive impedance to a relatively low value so as to produce a relatively low voltage drop during the switching operation. As soon as the switching operation has been completed the reactor l2 and the reactor I4 will be short circuited and the reactor II will carry the relatively small current produced by the voltage between the taps.

In Fig. 3 the winding I may be considered the primary winding of a transformer l5, which winding is supplied with current by the circuit 3. The transformer l5 may have a secondary winding I6 for supplying current to a load circuit l1. Alternate taps 2 on the winding l are connected to a pair of ratio adjusting switches 18 and I9, respectively, and the movable contacts of these switches are connected respectively to the fixed contacts 8" and 5" of the transformer current transferring switch 4". The bridging contact member I" of the switch 4", which is pivoted at point 8", has an extension which is connected with another pivoted lever 20 by means of a compression spring 2|. Lever 20 is adapted to be moved up and down by means of a connecting rod 22 connected to a crank pin 23 on a disk 24 which in turn is adapted to be rotated through suitable gearing by means of a reversible motor 25. The direction of operation of the motor 25 is controlled by raise" and "lower contacts 26 and 21, respectively, of a voltage sensitive relay or contact making voltmeter 28 which is connected to respond to the voltage of load circuit H by means of a potential transformer 29.

The disk 24 is provided with a pin 30 for cooperating with Geneva gears SI and 32 connected respectively to drive the movable contacts of the ratio changing switches I8 and IS.

The throws of the transformer current transferring switch 4" are shunted by negative resistance current characteristic resistances 9" and Ill", respectively, and also by saturable selfsaturating reactors l2" and I3". The cost per unit rating of reactors is less than negative characteristic resistors of the type suitable for use in my invention and consequently the reactors l2" and I3" may be designed to carry substantially all of the circuit current and the resistors 8" and Ill" are provided merely to prevent voltage peaks from occurring. Because of the fact that the current which is switched is alternating current the cores of the reactors l2" and I!" will be unsaturated when the current is passing through zero and as the rate of change of current at the zero point is relatively high, voltage peaks are likely to be produced at these times when heavy currents are being switched. However, these peak voltages are in eiIect chopped off by the negative characteristic resistances 9" and I8" because the resistance of these devices decreases rapidly as the voltage across them increases so that just before and after the zero current period the current will momentarily be carried by these resistances.

In the operation of Fig. 3 let it be assumed that the supply circuit 31s energized and that load is applied to the load circuit l1. Let it also be assumed that the voltage of load circuit I1 is lower than normal. This will cause the contact making voltmeter 28 to complete a circuit for the motor 25 through the raise contacts 26 thereby causing the motor to turn the disk 24 in a counterclockwise direction as viewed in the drawing. When the disk turns in this direction the pin 38 will cause the Geneva gear ll to turn through a given angle causing the ratio changing switch ii to make connection with its next right-hand tap. No current is flowing through the ratio changing switch at this time because the switch arm 'I" of the transfer switch is engaging the fixed contact 5" so that all of the current is flowing through the ratio changing switch it. However, as the disk 24 continues to rotate in a counter-clockwise direction and shortly after the Geneva gear 3i has operated the dial switch l8 the arm 20 will have its right-hand end moved below the lefthand end of the extension oi' the switch arm 'I" whereupon the spring 2i, whichhas been compressed, will rapidly snap the movable contact 1" from the fixed, contact 6" to the other fixed contact 8". The transformer current will thereupon be transferred from the ratio changing switch is to the ratio changing switch i8. During this transfer the operation of the switch 4" and the negative impedance-current characteristic impedances will be that which has already been described so that the current will not be interrupted and minimum voltage disturbances will occur in the circuit. The transferring of the currentfrom the ratio changing switch I! to the ratio changing switch IS in effect reduces the number of turns in the primary winding i with respect to the turns in the secondary winding i6 thereby increasing the voltage of the load circuit II. If this does not restore the voltage to normal the motor 25 will continue to operate and the pin 30 will next move the Geneva gear ii in a clockwise direction so as to cause clockwise motion of the dial switch IE to its next right-hand tap.

Shortly thereafter the arm 20 will have moved up 25 through the lower contacts 21 which will cause the motor to operate in thereverse direction thereby reversing the direction of rotation of the disk 24 whereby the dial switches will be operated alternately with the transformer current transferring switch 4" so as to increase the number of turns of the primary winding l and thus reduce the voltage of the load circuit IT.

From the above description of various embodiments of my invention it will be seen that during a current switching operation the current is carried by at least two impedances in parallel while at other times the tap voltage is applied to but one of the impedances at a time. Hence when the impedances are called upon momentarily to carry the main current they are connected in the circuit so as to present the minimum impedance, without regard to their negative characteristics, while at other times they are connected so as to present a much higher impedance to tap voltage produced circulating current,. also without regard to their negative characteristics.

While I have shown and described particular embodiments of my invention it will be obvious to those skilled in the art that changes and modifications may be made and I therefore aim in the appended claims to cover all such changes and v 7 3 modifications ascome within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an electric power circuit, switching means for selectively connecting a conductor which is included in said circuit to any one of a plurality of different points in said circuit, and a plurality of negative impedance-current characteristic impedances connected respectively between said conductor and said points.

2. In an electric power circuit, switching means for selectively connecting a conductor which is included in said circuit to any one of a plurality of points in said circuit, and a plurality of negative impedance-current characteristic impedances connected respectively between said conductor and said points, said impedances being capable of dividing the full load current of said circuit with relatively low voltage drop during a positional change of said switch and preventing the flow of all but a negligible current therethrough at other times.

3. In combination, a transformer winding having taps, a circuit conductor, switching means for selectively connecting said taps to said circuit conductor, and a plurality of negative impedancecurrent characteristic impedances connected respectively between said taps and said circuit conductor.

4. In combination, an alternating current circuit, a transformer having a winding provided with taps, a tap changing switch for selectively connecting two of said taps to one of the conductors of said circuit, and a pair of negative impedance-current characteristic impedances connected respectively between said taps and said circuit conductor, said impedances being so correlated to the circuit voltage, the tap voltage and to the transformer full load current that said current divides between said impedances with the production of a nominal voltage drop during a switch positional change while the current through said impedances caused by the voltage between said taps is negligible.

5. In combination, a transformer winding having taps, a tap changing switch having a movable contact member for selectively making contact with a pair of fixed contacts connected to different taps on said winding, and separate negative impedance-current characteristic impedances connected respectively between said fixed contacts and said movable contact member, the impedance of said impedances with respect to the voltage between said taps being suillciently high to limit the current therethrough to a negligible value, said impedances however being adapted to divide the full load current of said winding during a switch positional change with the produc-' switches and having a movable contact connected to a conductor of said circuit, and a pair of negative impedance-current characteristic impedances connected respectively between said fixed contacts and said conductor of said circuit.

' JOBII' W 

